What is a quadrupole mass spectrometer?
A quadrupole mass spectrometer consists of four parallel rods oriented like the four poles on a compass. The North-South pair have a radio frequency (rf) and direct current (dc) voltage of one polarity and the East -West pair have rf and dc voltages of opposite polarity. Hexapoles and octapoles are similar but have six and eight rods respectively. They are used as collision and/or storage cells. In tandem mass spectrometers such as triple quadrupoles or Q-Tofs the quadrupole functions as either a mass spectrometer or in an ion transmission mode. To acquire MS spectra the quadrupole is operated in the so-called rf mode in which it acts to transmit the ions from the ion source to the third quadrupole or the TOF where the spectrum is recorded. In daughter ion/product ion MS/MS mode the quadrupole is used in a static mode to select a particular ion for CAD (collision activated dissociation). The resulting MS spectrum can be used to determine a partial amino acid sequence of a peptide. In p
